Low density, rigid to semi-rigid polyurethane or polyisocyanurate foams have utility in a wide variety of insulation applications including roofing systems, building panels, building envelope insulation, spray applied foams, one and two component froth foams, insulation for refrigerators and freezers, and so called integral skin for application such as steering wheels and other automotive or aerospace cabin parts, shoe soles, and amusement park restraints. Critical to the large-scale commercial acceptance of rigid polyurethane foams is their ability to provide a good balance of properties. For example, rigid polyurethane and polyisocyanurate foams are known to provide outstanding thermal insulation, excellent fire resistance properties, and superior structural properties at reasonably low densities. Integral skin foams are known to produce a tough durable outer skin and a cellular, cushioning core.
It is known in the art to produce rigid or semi-rigid polyurethane and polyisocyanurate foams by reacting a polyisocyanate with one or more polyols in the presence of one or more blowing agents, one or more catalysts, one or more surfactants and optionally other ingredients. Blowing agents include hydrocarbons, fluorocarbons, chlorocarbons, chlorofluorocarbons, hydrochlorofluorocarbons, halogenated hydrocarbons, ethers, esters, aldehydes, alcohols, ketones, organic acid or gas, most often CO2, generating materials. Heat is generated when the polyisocyanate reacts with the polyol, and volatilizes the blowing agent contained in the liquid mixture, thereby forming bubbles therein. In the case of gas generating materials, gaseous species are generated by thermal decomposition or reaction with one or more of the ingredients used to produce the polyurethane or polyisocyanurate foam. As the polymerization reaction proceeds, the liquid mixture becomes a cellular solid, entrapping the blowing agent in the foam's cells. If a surfactant is not used in the foaming composition, the bubbles simply pass through the liquid mixture without forming a foam or forming a foam with large, irregular cells rendering it not useful.
The foam industry has historically used liquid fluorocarbon blowing agents because of their ease of use and ability to produce foams with superior mechanical and thermal insulation properties. Fluorocarbons not only act as blowing agents by virtue of their volatility, but also are encapsulated or entrained in the closed cell structure of the rigid foam and are the major contributor to the low thermal conductivity properties of the rigid urethane foams. Fluorocarbon-based blowing agents also produce a foam having a favorable k-factor. The k-factor is the rate of transfer of heat energy by conduction through one square foot of one-inch thick homogenous material in one hour where there is a difference of one degree Fahrenheit perpendicularly across the two surfaces of the material. Since the utility of closed-cell polyurethane-type foams is based, in part, on their thermal insulation properties, it would be advantageous to identify materials that produce lower k-factor foams.
Preferred blowing agents also have low global warming potential. Among these are hydrohaloolefins including hydrofluoroolefins of which trans-1,3,3,3-tetrafluoropropene (1234ze(E)) and 1,1,1,4,4,4hexafluorobut-2-ene (1336mzzm(Z)) are of particular interest and hydrochlorofluoroolefins of which trans-1-chloro-3,3,3-trifluoropropene (1233zd(E)) is of particular interest. Processes for the manufacture of trans-1,3,3,3-tetrafluoropropene are disclosed in U.S. Pat. Nos. 7,230,146 and 7,189,884. Processes for the manufacture of trans-1-chloro-3,3,3-trifluoropropene are disclosed in U.S. Pat. Nos. 6,844,475 and 6,403,847.
It is convenient in many applications to provide the components for polyurethane or polyisocyanurate foams in pre-blended formulations. Most typically, the foam formulation is pre-blended into two components. The polyisocyanate and optionally isocyanate compatible raw materials, including but not limited to certain blowing agents and non-reactive surfactants, comprise the first component, commonly referred to as the “A” component. A polyol or mixture of polyols, one or more surfactant, one or more catalyst, one or more blowing agent, and other optional components including but not limited to flame retardants, colorants, compatibilizers, and solubilizers comprise the second component, commonly referred to as the “B” component. Accordingly, polyurethane or polyisocyanurate foams are readily prepared by bringing together the A and B side components either by hand mix for small preparations and, preferably, machine mix techniques to form blocks, slabs, laminates, pour-in-place panels and other items, spray applied foams, froths, and the like. Optionally, other ingredients such as fire retardants, colorants, auxiliary blowing agents, and other polyols can be added to the mixing head or reaction site. Most conveniently, however, they are all incorporated into one B component.
Applicants have come to appreciate that a shortcoming of two-component systems, especially those using certain hydrohaloolefins, including 1234ze(E), 1336(Z), and 1233zd(E), is the shelf-life of the B-side composition. Normally when a foam is produced by bringing together the A and B side components, a good foam is obtained. However, applicants have found that if the polyol premix composition containing a halogenated olefin blowing agent and a typical amine-containing catalyst is aged, prior to treatment with the polyisocyanate, deleterious effects can occur. For example, applicants have found that such formulations can produce a foamable composition which has an undesirable increase in reactivity time and/or a subsequent cell coalescence. The resulting foams are of lower quality and/or may even collapse during the formation of the foam.